Many pourable food products, such as fruit juice, UHT milk, wine, tomato sauce, etc., are sold in packages made of sterilized packaging material.
A typical example of such a package is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik or Tetra Brik Aseptic (registered trademarks), which is formed by folding and sealing laminated strip packaging material.
The packaging material has a multilayer structure comprising a layer of fibrous material, e.g. paper, covered on both sides with layers of heat-seal plastic material, e.g. polyethylene.
In the case of aseptic packages for long-storage products, such as UHT milk, the packaging material also comprises a layer of barrier material defined, for example, by an aluminium film, which is superimposed on a layer of heat-seal plastic material and is in turn covered with another layer of heat-seal plastic material eventually defining the inner face of the package contacting the food product.
As is known, such packages are made on fully automatic packaging machines, on which a continuous tube is formed from the packaging material supplied in strip form; and the strip of packaging material is sterilized on the packaging machine, e.g. by applying a chemical sterilizing agent, such as a hydrogen peroxide solution.
After sterilization, the sterilizing agent is removed, e.g. vaporized by heating, from the surfaces of the packaging material; and the strip of packaging material so sterilized is maintained in a closed sterile environment, and is folded and sealed longitudinally to form a tube.
The tube is filled with the sterilized or sterile-processed food product, and is sealed and cut at equally spaced cross sections to form pillow packs, which are then folded mechanically to form the finished, e.g. substantially parallelepiped-shaped, packages.
Along the path of the strip of packaging material, packaging machines of the above type normally comprise a number of photocells facing, and for detecting the passage of optically detectable elements on, the strip, e.g. optical register or reference codes, in particular bar codes, printed on the strip.
The photocells are connected to a control unit for controlling the packaging machine, and which acquires the signals generated by the photocells and, in known manner, accordingly enables the performance of specific operations on the strip of packaging material.
Photocells currently available on the market are also self-setting to adapt to specific operating conditions, by implementing a teach-in procedure, which can be enabled either in local mode—i.e. by the operator pressing a button on the photocell—or in centralized or remote mode—i.e. by means of an enable signal from the control unit to an input on the photocell.
The teach-in procedure requires that a register code be fed past each photocell, which is done manually by the operator either feeding the strip of packaging material past each photocell, or using a register code impressed on a separate sheet of paper.
The teach-in procedure provides for automatically setting photocell operating parameters such as: light spot color (red, green, blue) used to detect passage of the register code on the strip of packaging material and static intervention threshold.
Though extremely advantageous costwise, photocells of the above type, when used on packaging machines, pose several drawbacks preventing full use of the advantages available.
In particular, local mode enabling the teach-in procedure of each individual photocell takes a relatively long time, on account of both the large number of photocells involved and the actual location of the photocells, which, on packaging machines, are not always easily accessible by the operator.
Though faster than local mode, centralized enabling of the teach-in procedure is also far from negligible by still involving a fairly considerable amount of downtime.